Video camera system with interchangeable lens assembly

ABSTRACT

A camera system includes a camera body and an interchangeable lens attachable to and detachable from the camera body. Within the camera body, an image signal is generated representing a picture. A prescribed signal component is extracted from the image signal, and an evaluation value relating to an imaged state of said picture is generated. For example, a focal-point evaluation value is extracted by an AF signal processing circuit from an image signal corresponding to a distance measurement frame. The distance measurement frame is set by a distance measurement frame controller by detecting the photographers line-of-sight. These evaluation values are then transmitted from the camera body to the lens assembly. In this manner, for example, a zoom lens and a focusing lens may then be controlled by the lens assembly in response to the evaluation value.

BACKGROUND OF THE INVENTION

This invention relates to a lens assembly and an image sensing deviceideal for use in a video camera system of the type having aninterchangeable lens assembly.

Automatic focusing (AF) used in video equipment such as video camerarelies upon the so-called “hill-climbing method” according to whichfocusing is performed by extracting high-frequency components from avideo signal obtained from an image sensing device such as a CCD anddriving a camera lens so as to maximize a mountain-shaped curverepresenting the characteristic of the high-frequency components.

This automatic focusing method is advantageous in that special opticalmembers for focusing are not required and focusing can be performedaccurately regardless of whether distance to the subject is long orshort.

An example in which such an automatic focusing method is used in a videocamera whose lens assembly can be interchanged will be described withreference to FIG. 9.

A conventional variable-power lens assembly 916 includes avariable-power lens 902 and a compensating lens 903 mechanicallyconnected by a cam. When zooming is performed manually or under power,the variable-power lens 902 and compensating lens 903 move in unison.The variable-power lens 902 and compensating lens 903 are collectivelyreferred to as zoom lenses. In a lens system of this type, a front lens901, which is situated closest to the subject, serves as the focusinglens and is moved along the optic axis to perform focusing.

Light that has passed through this group of lenses forms an image on theimage sensing surface of an image sensing device 904 in a camera body917, whereby the incident light is photoelectrically converted to anelectric signal and outputted as a video signal.

The video signal is applied to a CDS/AGC circuit 905, which is composedof a correlated dual-sampling circuit and an automatic gain controlcircuit. The CDS/AGC circuit 905 samples and holds the video signal andthen amplifies the signal to a predetermined level. The amplified signalis converted to digital video data by an A/D converter 906 and thesedata are then applied to a processing circuit, which is the next stageof the camera, to be converted to a standard television signal.

The video signal that has been converted to the digital video data bythe A/D converter 906 enters a bandpass filter (hereinafter referred toas a “BPF”) 907.

The BPF 907 extracts high-frequency components, the level of whichchanges in dependence upon the state of focusing, from the video signal,and a gate circuit 908 picks out only a signal that corresponds to aportion that has been set on a focal-point detection area on a screenpicture. A peak-hold circuit 909 holds the peak of the signal atintervals synchronized to a whole-number multiple of a verticalsynchronizing signal and generates a focus (AF) evaluation value.

This AF evaluation value is accepted by an AF microcomputer 910 in thecamera body 917. The AF microcomputer 910 decides a focusing motor speedconforming to the degree of focusing and decides focusing motor drivedirection in such a manner that the AF evaluation value will increase.The speed and direction of the focusing motor are sent to a lensmicrocomputer 911.

The lens microcomputer 911 performs focusing by driving the focusinglens 901 along the optic axis, this being achieved by driving a motor913 via a motor driver 912 in response to a command from themicrocomputer 910.

The microcomputer 910 decides the driving direction and speed of thezoom lenses 902, 903 in conformity with the status of a zoom switch 918and sends these signals to a zoom motor driver 914 in the lens assembly916 to drive the zoom lenses 902, 903 via a zoom motor 915.

The camera body 917 is detachable from the lens assembly 916 so that adifferent lens assembly may be connected.

The image sensing apparatus shown in FIG. 9 is capable of having itslenses interchanged and for this reason the controls for automaticfocusing are provided in the camera 917. Consequently, when the responseof automatic focusing is decided so as to be optimum for a specificlens, there are occasions where the respones will not be optimum foranother lens. It is difficult to realize optimum performance with regardto all lenses capable of being attached to the camera.

The applicant has previously proposed an image sensing apparatus inwhich the controls for automatic focusing are provided on the side ofthe lens assembly and a focusing signal necessary for the purpose ofexecuting focusing control is delivered from the body of the imagesensing apparatus to the lens assembly.

Automatic focusing described above relies upon a mechanism in which theimage sensing apparatus such as a camera automatically judges thephotographic conditions and adjusts lens position to achieve a stateconstrued to be suited to the photographic conditions. As a result,situations can arise in which the intentions of the photographer are notreflected in the video obtained.

For example, consider a situation in which a subject in the distance anda subject close by are both present in the area of the screen picture.If automatic focusing is performed on the basis of informationrepresenting the entirety of the screen picture in which the images arecurrently appearing, one of the plurality of subjects mentioned abovewill be brought into focus. However, the image sensing apparatus cannotdetermine whether this is the main subject that the photographer wishesto focus upon. In order to avoid such situations as much as possible,the general practice is to use a technique in which emphasis is placedupon measuring the distance to the subject located at the center of thescreen picture (this is referred to as “weighted-center distancemeasurement”) and automatic focusing is executed based upon the resultsof measurement.

The reason for this is that when the photograph performs photography,often the main subject is located in the center of the picture. However,if the main subject is located somewhere other than the center of thepicture, there are instances where focusing cannot be carried outproperly with respect to the main subject. This is the chiefdisadvantage of this system.

To improve upon this, the specification of Japanese Patent ApplicationNo. 4-1541656 discloses an image sensing apparatus in which thephotographer looking at the finder is capable of selecting the mainsubject by his or her line of sight in such a manner that the mainsubject will be brought to the best focus regardless of where it islocated in the screen picture. In accordance with this line-of-sightposition detection distance measurement method, it is possible for theposition of the main subject to be changed at will while limiting thedistance measurement area.

The positioning designating means for selecting the main subject is notlimited to line-of-sight detecting means. For example, it is possible toconceive of position designating means which decides direction ofmovement and position by synthesizing amount of movement in twodimensions using a pointing device such as a joystick or mouse.

In general, the distance measurement area in the weighted-centerdistance measurement” method is set to be large relative to the screenin such a manner that a subject not located in the center will befocused appropriately. With the line-of-sight position detectiondistance measurement method, the distance measurement area is set to besmall relative to the screen so that competing subjects near and farwill not coexist in the distance measurement area. This is so that thecamera can be directed toward the main subject to achieve optimum focusregardless of where the main subject is located in the screen picture.

However, when it is attempted to realize the function for selecting themain subject with the interchangeable-lens image sensing apparatushaving the automatic focusing controls provided in the lens assembly,the distance measurement area on the screen changes in conformity with achange in the position of the main subject and so does the focusingsignal extracted from the distance measurement area. Accordingly,whether a change in the focusing signal is ascribable to a change in thesubject distance that accompanies a camera operation such as panning orto a change in the distance measurement area that accompanies a changein the position of the main subject cannot be distinguished merely bydelivering the focusing signal from the body of the image sensingapparatus to the focusing control section of the lens assembly.

For example, when a person walking from left to right on the screen isfollowed by position designating means described above, the focusingsignal changes with movement of the subject even though there is nochange in the distance to the subject. As a consequence, the lensmicrocomputer performs a focusing operation upon erroneously judgingthat the subject has gone out of focus. This causes inadvertent blurringof the subject.

Further, in the example described above, the lens assembly is incapableof recognizing the distance measurement method. Consequently, theautomatic focusing operation is unstable in the line-of-sight positiondetection distance measurement method, the foundation of which is asmall distance measurement area that is readily susceptible to theinfluence of camera operation and changes in the subject, the result ofwhich is frequent changes in the focusing signal. Thus, if an attempt ismade to control automatic focusing on the side of the lens assembly inthe camera system described above, many problems arise in terms ofcontrol between the camera and lens assembly.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a lensassembly and image sensing apparatus in which a desired subject among avariety of subjects can be focused stably under a variety ofphotographic conditions even when various lens assemblies are attached.

A video camera system according to the present invention, a cameraconstituting a part of this system and a lens assembly are characterizedby the elements described below.

Specifically, a camera having an interchangeable lens assembly capableof processing an image signal comprises pointing means for pointing toany position on a screen of the camera, area setting means for setting aprescribed area at any position pointed to by the pointing means,extracting means for extracting a prescribed signal component from animage signal contained in the above-mentioned image signal andcorresponding to the prescribed area set by the area setting means, andgenerating an evaluation value relating to the imaging state of thescreen, and transmitting means for transmitting information relating toan prescribed area, information representing status of the area settingmeans and the evaluation value to the lens assembly.

In a preferred embodiment, the prescribed area is a focal-pointdetecting area for detecting a focal point of the lens assembly, and theevaluation value relating to an imaged state represents state of focusof the lens assembly.

In a preferred embodiment, the pointing means adopts a position as theabove-mentioned any position by detecting line of sight of the operatordirected into the screen.

By way of example, the camera may be provided with one more area settingmeans for setting a focal-point detecting area at a predeterminedposition on the screen, with either of the area setting means beingselectable by selecting means.

Further, a lens assembly capable of being attached to and detached froma camera comprises drive means for driving a lens possessed by the lensassembly, receiving means for receiving, from the camera, an evaluationvalue relating an imaging state of the screen, information relating to aset area on the screen and information representing operation of the setarea, and control means for controlling the drive means based upon theevaluation value, the information relating to the set area and theinformation representing the operation of the set area received from thereceiving means.

In a preferred embodiment, the set area is a focal-point detecting areafor detecting the focal point of the lens assembly, and the evaluationvalue relating the imaging state represents state of focus of the lensassembly.

In a preferred embodiment the information representing the operation ofthe set area indicates whether the focal-point detection area iscurrently changing, and the control means inhibits a control operationduring a change in the focal-point detection area and changes thecontrol operation to a prescribed operation when the change in thefocal-point detection area has ended.

In the camera and lens assembly constructed as set forth above, an imagesignal captured by the camera and the information relating to the setarea on the screen are transmitted to the lens assembly, and the settingof the prescribed area and generation of the evaluation value relatingto the imaging state of the screen may be performed not by the camerabut by the lens assembly based upon the information transmitted. In thiscase the image signal is normalized by the camera before it istransmitted to the lens unit.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a first embodiment in which thepresent invention is applied to a video camera with an interchangeablelens;

FIG. 2 is a block diagram illustrating the elements of an AF signalprocessing circuit on the side of a camera body in the first embodimentof the invention;

FIG. 3 is a diagram for describing the detection timing of variousfocal-point evaluation values;

FIG. 4 is a diagram for describing the resetting of signals in variousdistance measurement frames set on a screen as well as data transfertiming;

FIG. 5 is a diagram for describing an operation for resetting a distancemeasurement frame that conforms to a change in line-of-sight detectionposition on the screen as well as the timing of a data transferoperation;

FIG. 6 is a flowchart illustrating an AF control operation performed onthe side of the lens assembly;

FIGS. 7A to 7D are diagrams for describing a change in focal-pointevaluation value versus movement of a focusing lens and for explaining awobbling operation;

FIG. 8 is a block diagram illustrating a video camera with aninterchangeable lens according to a modification of the firstembodiment;

FIG. 9 is a block diagram illustrating an example of a video camera withan exchangeable lens according to the prior art;

FIG. 10 is a block diagram illustrating a second embodiment in which theinvention is applied to a video camera with an interchangeable lens;

FIG. 11 is a block diagram illustrating the elements of an AF signalprocessing circuit on the side of a camera body in the second embodimentof the invention; and

FIG. 12 is a block diagram illustrating a modification of the secondembodiment in which the invention is applied to a video camera with aninterchangeable lens.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described in detailwith reference to the drawings.

FIG. 1 is a block diagram illustrating the construction of a firstembodiment of the present invention. A lens assembly 127 and a camerabody 128 are capable of being detached and construct a so-calledinterchangeable lens assembly system.

Light from a subject forms an image on the image sensing surfaces ofimage sensing devices 106˜108 such as CCDs through a first lens group101 that is fixed, a second lens group 102 for performing zooming, adiaphragm 103, a third lens group 104 that is fixed and a fourth lensgroup 105 (hereinafter referred to as a focusing lens) having a both afocusing function and a compensating function, which compensates formovement of the focal plane due to zooming.

The red component of the three component colors forms an image on theimage sensing device 106, the green component forms an image on theimage sensing device 107 and the blue component forms an image on theimage sensing device 108.

The images formed on the image sensing surfaces of the respective imagesensing devices 106˜108 are photoelectrically converted to imagesignals. The image signals are amplified to optimum levels by respectiveamplifiers 109, 110, 111, the amplified signals enter a camera signalprocessing circuit 112 to be converted to a standard television signal,the television signal is amplified to a predetermined level by anamplifier 132, and the amplified television signal is displayed as thesensed image on a finder of a liquid crystal monitor 134 via an LCDdisplay circuit 133.

This embodiment is provided with a line-of-sight detecting device fordetecting the line of sight of the operator on the finder screenpicture. The point gazed at in the finder is detected as set forthbelow.

An IRED (infrared ray emitting diode) driver 136 drives an IRED 135 by acontrol signal from a line-of-sight detecting circuit 140. Infraredlight emitted by IRED 135 is reflected by an eyeball 142 and thereflected infrared light has its optical path changed via a dichroicmirror (not shown), which reflects only the infrared light. As a result,the reflected infrared light impinges upon an image sensor 137, such asa CCD, provided for the purpose of detecting line of sight.

A circuit 138 drives the CCD image sensor 137 so that the infrared lightreflected by the eyeball 142 is converted to an electric signal via thesensor 137. The resulting electric signal is sent to the line-of-sightdetecting circuit 140 again via an amplifier 139.

The eyeball 142 observes the liquid crystal monitor 134 displaying thecaptured picture. What position on the display screen of the liquidcrystal monitor 134 is being looked at by the eyeball 142 can bedetected by the line-of-sight detecting device (which corresponds topointing means constituting a feature of the present invention)constituted by the line-of-sight detecting circuit 140.

By virtue of the line-of-sight detecting device described above, thecoordinates of the line-of-sight position are detected from the outputsignal of the amplifier 139 and the coordinates are transmitted asline-of-sight coordinate information from the line-of-sight detectingcircuit 140 to a distance measurement frame controller 129 in amicrocomputer 114, which is provided in the camera body 128.

In accordance with the status of a line-of-sight detection mode switch141, the distance measurement frame controller 129 decides the positionand size of a distance measurement frame (a focal-point detection areais described by being referred to as the distance measurement area) onthe finder screen picture using the line-of-sight position informationfrom the line-of-sight detecting circuit 140. The distance measurementframe information thus decided is read out in accordance with a datareadout program in the microcomputer 114 and the information istransmitted to an AF (autofocus) signal processing circuit 113. Thedistance measurement frame controller 129 corresponds to area settingmeans constituting a feature of the present invention.

The AF signal processing circuit 113 extracts an AF evaluation value inthe distance measurement frame. In order for the photographer to benotified of the point currently being looked at in the line-of-sightdetection mode, a video signal and a signal for displaying the distancemeasurement frame are mixed by the LCD display circuit 133 to display aline-of-sight frame on the liquid crystal monitor 134.

In a case where the line-of-sight detection mode has not been selectedby the line-of-sight detection mode switch 141, the distance measurementframe controller 129 decides the position and size of the distancemeasurement frame in such a manner that center-weighted distancemeasurement is performed emphasis is given to measuring the distance tothe subject at the central portion of the screen, sends theline-of-sight detecting circuit 140 information that inhibits theline-of-sight input function and inhibits the display of the distancemeasurement frame. As a result, the line-of-sight frame is not displayedon the liquid crystal monitor 134. The line-of-sight detection modeswitch 141 corresponds to selecting means which, according to a featureof the present invention, selects a focus area.

The video signal that enters the camera signal processing circuit 112enters the AF signal processing circuit 113 at the same time. The AFevaluation value generated by the AF signal processing circuit 113 isread out in accordance with the data readout program 115 in themicrocomputer 114 and is transferred to a lens microcomputer 116together with information indicating in which distance measurement framestate the evaluation value has been extracted (namely informationindicating the line-of-sight input ON/OFF status of the line-of-sightdetection mode switch 141 and information indicating the point beinglooked out, which information is obtained from the line-of-sightdetecting circuit 140).

The microcomputer 114 reads in the states of a zoom switch 130 and an AFswitch 131 and sends signals indicative of these states to the lensmicrocomputer 116.

It should be noted that this transmission of the information such as thefocal-point evaluation value and status of the distance measurementframe is implemented by communication functions possessed by the lensmicrocomputer 116 on the side of the lens unit 127 and the microcomputer114 in the camera body. These communication functions correspond totransmitting means and receiving means of the present invention. Thelens microcomputer 116 corresponds to control means for performingactual focusing control in the present invention.

When the AF switch 131 is open (OFF) and the zoom switch 130 is beingpressed, the lens microcomputer 116, on the basis of the informationreceived from microcomputer 114 in the camera body and in accordancewith a computer zoom program 119, sends a signal to a zoom motor driver122 to drive the motor in the telephoto or wide-angle direction,depending upon the direction in which the zoom switch 130 is beingpressed. As a result, the zoom lens 102 is driven via the zoom motor121. At the same time, the lens microcomputer 116 refers to lens camdata 120 and sends a signal to a focusing motor driver 126 to drive thefocusing lens 105 via a focusing motor 125 so that a compensatingoperation that eliminates blurring can be executed. Zooming isimplemented by these operations. It should be noted that the focusinglens 105, focusing motor driver 126 and focusing motor 125 correspond todrive means constituting a feature of the present invention.

More specifically, when a zooming operation is performed by driving azoom lens in an inner-focus type lens assembly, driving of the zoom lensis accompanied by a change in the position of the focal point. Thismeans that a compensating function is necessary to drive the focusinglens and compensate for the change in the position of the focal point.

The lens cam data 120 are obtained by storing a plurality of curveswhich indicate a change in focal-point position per each subjectdistance when the zoom lens is driven. On the basis of zoom lensposition and focusing lens position, the computer zoom block (program)119 refers to the plurality of curves of the stored lens cam data 120and specifies the corresponding curve, thereby deciding the drivingspeed and driving direction of the focusing lens 105.

In a case where the focusing lens is situated at a position not storedin the lens cam data 120, a curve that would be situated between curvesis calculated from the plurality of curves to set the curve in virtualfashion and implement control.

When the AF switch 131 is closed (turned ON) and the zoom switch 130 isheld depressed, it is required that the focused state be maintained.Therefore, in accordance with the computer zoom program 119, the lensmicrocomputer 116 refers to the AF evaluation value sent from themicrocomputer 114 in the camera body and performs the zooming operationwhile maintaining the position at which the AF evaluation signal ismaximized.

Further, when the AF switch 131 is turned on and the zoom switch is notbeing held depressed, the lens microcomputer 116, in accordance with anAF program 117, performs an automatic focusing operation by sending asignal to the focusing motor driver 126 to drive the focusingcompensating lens 105 via the focusing motor 125 in such a manner thatthe AF evaluation value sent from the microcomputer 114 is maximized.

The AF signal processing circuit 113 in the camera signal processingcircuit 112 will now be described with reference to FIG. 2. The AFsignal processing circuit 113 corresponds to extracting means forextracting the focal-point evaluation value in accordance with a featureof the invention.

The outputs of the R (red), G (green), B (blue) image sensing devicesapplied to respective optimum levels by the amplifiers 109, 110, 111,respectively, are supplied to the AF signal processing circuit 113,where these outputs are converted to digital signals by A/D converters206, 207, 208, respectively. The digital signals are applied to thecamera signal processing circuit 112 and, at the same time, areamplified to appropriate levels by amplifiers 209, 210, 211,respectively. The amplified signals are added by an adder 208, theoutput of which is a luminance signal S5 for automatic focusing.

The luminance signal S5 enters a gamma circuit 213 and applies a gammaconversion in accordance with a gamma curve set in advance, whereby asignal S6 whose low-luminance components are emphasized andhigh-luminance components are suppressed. This signal S6 resulting fromthe gamma conversion enters a TE-LPF 214, which is a high-pass filter(hereinafter referred to as an “LPF”) with respect to cut-off frequency,and an FE-LPF 215, which is an LPF with respect to cut-off frequency.These LPFs extract low-frequency components based upon respective filtercharacteristic information decided by the microcomputer 114 via amicrocomputer interface 253. The TE-LPF 214 produces an output signal S7and the FE-LPF 215 an output signal S8.

The signals S7 and S8 are switched between selectively by a switch 216in dependence upon a Line E/O signal, which is a signal for identifyingwhether a horizontal line in one screen is an odd-numbered oreven-numbered line. The selected signal is applied to a bypass filter(hereinafter referred to as an “HPF”) 217.

More specifically, the signal S7 is supplied to the HPF 217 in case ofan odd-numbered line and the signal S8 is supplied to the HPF 217 incase of an even-numbered line.

The HPF 217 extracts only high-frequency components based uponrespective filter characteristic information for each of the odd- andeven-numbered lines decided by the microcomputer 114 via themicrocomputer interface 253. An absolute-value circuit 218 takes theabsolute value of this signal, thereby producing a positive signal S9.More specifically, the signal S9 alternately indicates the level of thehigh-frequency components extracted by filters whose filtercharacteristics differ for the even- and odd-numbered lines. As aresult, high-frequency components which differ can be obtained byscanning one screen.

The timing at which various information is accepted within the AF signalprocessing circuit 113 will be described with reference to FIG. 3, whichillustrates the layout of each area for focal-point detection on thescreen. The outer frame is the effective image screen of the outputsfrom the image sensing devices 106, 107, 108.

The three partitioned inner frames are gate frames for focal-pointdetection. A frame L on the left side, a frame C at the center and anframe R on the right side are formed in accordance with an frame Lgenerating gate signal, a frame C generating gate signal and an frame Rgenerating gate signal, respectively, outputted by a frame generatingcircuit 254.

A reset signal is outputted for each of the L, C, R frames at thestarting point of each of the L, C, R frames, initialization (reset)signals LR1, CR1, RR1 are generated and integrating circuits 232˜237,peak-hold circuits 219˜221, 225˜227, 247˜249, etc., are reset.

A data transfer signal IR1 is generated at the end of scanning of thefocal-point detection area comprising the L, C, R frames, and theintegrated values from the integrating circuits and peak-hold valuesfrom the peak-hold circuits are transferred to respective buffers.

The scanning of even fields is indicated by solid lines, the scanning ofodd fields is indicated by dashed lines, even lines select the TE-LPFoutput and odd lines select the FE-LPF output for both the even and oddfields.

The signal S9 is supplied to the peak-hold circuits 225, 226 and 227,which are for holding the peak values of the signals in the L, C and Rframes, respectively, the peak values of the high-frequency componentsin the respective frames are detected and enter a line peak-hold circuit231 so that the peak value of each horizontal line is detected.

In accordance with a command supplied by the microcomputer 114 via themicrocomputer interface 253, the frame generating circuit 254 generatesthe gate signals L, C, R for forming the focal-point adjustment L, C,and R frames at the positions on the screen shown in FIG. 3.

The gate signal L for forming the frame L outputted by the framegenerating circuit 254 and the Line E/O signal (produced by themicrocomputer 114), which is the signal for identifying whether ahorizontal line is even- or odd-numbered, enter the peak-hold circuit225. The peak-hold circuit 225 is initialized at the location of LR1 atthe upper left or starting point of the focal-point adjustment frame L,as shown in FIG. 3, and holds the peak of the signal S9 of each frame ofeither even or odd lines designated by the microcomputer 114 via themicrocomputer interface 253. At IR1 at the lower right, i.e., whenscanning of the entire area for focal-point adjustment ends, thepeak-hold circuit 225 transfers the peak-hold value within the frame toan area buffer 228, whereby a TE/FE peak evaluation value is generated.

Similarly, the frame C outputted by the frame generating circuit 254 andthe Line E/O signal enter the peak-hold circuit 226. The peak-holdcircuit 226 is initialized at the location of CR1 at the upper left orstarting point of the focal-point adjustment frame C, as shown in FIG.3, and holds the peak of the signal S9 of each frame of either even orodd lines designated by the microcomputer 114 via the microcomputerinterface 253. At IR1 at the lower right, i.e., when scanning of theentire area for focal-point adjustment ends, the peak-hold circuit 226transfers the peak-hold value within the frame to an area buffer 229,whereby a TE/FE peak evaluation value is generated.

Similarly, the frame R outputted by the frame generating circuit 254 andthe Line E/O signal enter the peak-hold circuit 227. The peak-holdcircuit 227 is initialized at the location of RR1 at the upper left orstarting point of the focal-point adjustment frame C, as shown in FIG.3, and holds the peak of the signal S9 of each frame of either even orodd lines designated by the microcomputer 114 via the microcomputerinterface 253. At IR1 at the lower right, i.e., when scanning of theentire area for focal-point adjustment ends, the peak-hold circuit 227transfers the peak-hold value within the frame to an area buffer 230,whereby a TE/FE peak evaluation value is generated.

The signal S9 and the gate signals for generating the L, C, F framesoutputted by the frame generating circuit 254 enter the line peak-holdcircuit 231, this circuit is initialized at the starting point of eachframe in the horizontal direction, and the peak value contained in oneline of the signal S9 in the horizontal direction within each frame isheld.

The output of the line peak-hold circuit 231 and the Line E/O signal,which identifies whether the horizontal line is odd- or even-numbered,enter the integrating circuits 232, 233, 234, 25, 236, 237. At the sametime, the gate signal for generating the frame L outputted by the framegenerating circuit 254 enters the integrating circuits 232, 235, thegate signal for generating the frame C outputted by the frame generatingcircuit 254 enters the integrating circuits 233, 236, and the gatesignal for generating the frame R outputted by the frame generatingcircuit 254 enters the integrating circuits 234, 237.

The integrating circuit 232 is initialized at LR1 at the upper left orstarting point of the focal-point adjustment frame L and adds the outputof the line peak-hold circuit 231 to an internal register immediatelybefore the end of even lines in each frame. At IR1, the integratingcircuit 232 transfers the peak-hold value within the frame to an areabuffer 238, whereby a line-peak integration evaluation value isgenerated.

The integrating circuit 233 is initialized at CR1 at the upper left orstarting point of the focal-point adjustment frame C and adds the outputof the line peak-hold circuit 231 to an internal register immediatelybefore the end of even lines in each frame. At IR1, the integratingcircuit 233 transfers the peak-hold value within the frame to an areabuffer 239, whereby a line-peak integration evaluation value isgenerated.

The integrating circuit 234 is initialized at RR1 at the upper left orstarting point of the focal-point adjustment frame R and adds the outputof the line peak-hold circuit 231 to an internal register immediatelybefore the end of even lines in each frame. At IR1, the integratingcircuit 233 transfers the peak-hold value within the frame to an areabuffer 240, whereby a line-peak integration evaluation value isgenerated.

In the same manner that the above-mentioned integrating circuits 232,233, 234 perform addition with regard to the data of even lines, theintegrating circuits 235, 236, 237 perform addition of data of the oddlines. In other aspects the operation of these integrating circuits isthe same as that of the integrating circuits 232, 233, 234 and theresults are transferred to area buffers 241, 242, 243, respectively.

The signal S7 enters the peak-hold circuits 219, 220, 221, a linemaximum-value hold circuit 244 and a line minimum-value hold circuit245.

The gate signal for generating the frame L outputted by the framegenerating circuit 254 enters the peak-hold circuit 219. The peak-holdcircuit 219 is initialized at LR1 at the upper left or starting point ofthe frame L and holds the peak of the signal S7 in each frame. At IR1,the peak-hold circuit 219 transfers results of peak hold to a buffer222, whereby a luminance level (hereinafter referred to as a “Y signal”)peak evaluation value is generated.

Similarly, the gate signal for generating the frame C outputted by theframe generating circuit 254 enters the peak-hold circuit 220. Thepeak-hold circuit 220 is initialized at CR1 at the upper left orstarting point of the frame C and holds the peak of the signal S7 ineach frame. At IR1, the peak-hold circuit 220 transfers results of peakhold to a buffer 223, whereby a Y-signal peak evaluation value isgenerated.

Similarly, the gate signal for generating the frame R outputted by theframe generating circuit 254 enters the peak-hold circuit 221. Thepeak-hold circuit 221 is initialized at RR1 at the upper left orstarting point of the frame R and holds the peak of the signal S7 ineach frame. At IR1, the peak-hold circuit 221 transfers results of peakhold to a buffer 224, whereby a Y-signal peak evaluation value isgenerated.

The gate signals for generating the L, C, R frames outputted by theframe generating circuit 254 enter the line maximum-value hold circuit244 and line minimum-value hold circuit 245, which are initialized atthe starting point of each frame in the horizontal direction and holdthe maximum and minimum values, respectively, contained in the Y signalof one horizontal line of signal S7 in each frame.

The maximum and minimum values of the Y signal held by the linemaximum-value hold circuit 244 and line minimum-value hold circuit 245,respectively, enter a subtractor 246. The latter produces a signal S10representing contrast, namely the difference between the maximum valueand the minimum value, and applies the signal S10 to the peak-holdcircuits 247, 248, 249.

The gate signal for generating the frame L outputted by the framegenerating circuit 254 enters the peak-hold circuit 247. The peak-holdcircuit 247 is initialized at LR 1 at the upper left or starting pointof the frame L and holds the peak of the signal S 10 in each frame. AtIR1, the peak-hold circuit 247 transfers results of peak hold to abuffer 250, whereby a Max-Min evaluation value is generated.

Similarly, the gate signal for generating the frame C outputted by theframe generating circuit 254 enters the peak-hold circuit 248. Thepeak-hold circuit 248 is initialized at CR1 at the upper left orstarting point of the frame C and holds the peak of the signal S10 ineach frame. At IR1, the peak-hold circuit 248 transfers results of peakhold to a buffer 251, whereby a Max-Min evaluation value is generated.

Similarly, the gate signal for generating the frame R outputted by theframe generating circuit 254 enters the peak-hold circuit 249. Thepeak-hold circuit 249 is initialized at RR1 at the upper left orstarting point of the frame R and holds the peak of the signal S10 ineach frame. At IR1, the peak-hold circuit 249 transfers results of peakhold to a buffer 252, whereby a Max-Min evaluation value is generated.

At IR1, which is when scanning of the entire vocal-point detection areacomprising the frames L, C, R ends, the data in each frame aretransferred to the respective buffers 222, 223, 224, 228, 229, 230, 238,239, 240, 241, 242, 243, 250, 251, 252 and, at the same time, the framegenerating circuit 254 sends an interrupt signal to the microcomputer114 and the data that have been transferred to each buffer aretransferred to the microcomputer 114.

More specifically, upon receiving the interrupt signal, themicrocomputer 114 reads the data in each of the buffers 222, 223, 224,228, 229, 230, 238, 239, 240, 241, 242, 243, 250, 251, 252 via themicrocomputer interface 253 until the scanning within the next frame L,frame C, frame R is completed and the next item of data is transferredto each buffer, and transfers the read data to the lens microcomputer116 in sync with a vertical synchronizing signal in a manner describedlater.

The lens microcomputer 116 calculates these focal-point evaluationvalues, detects the state of focusing, computes the driving speed anddriving direction of the focusing motor and controls the drive of thefocusing motor, thereby driving the focusing lens 105.

A method of setting positions at which the reset signals LR1, CR1, RR1in each of the frames L, C, R are generated as well as a position atwhich the data transfer signal IR1 is generated will now be describedwith reference to FIGS. 4 and 5.

The position of a point being stared at obtained from the line-of-sightdetecting circuit 140 corresponds to a coordinate position on the screenpicture [a point 401 (=x,y) on coordinate axes the origin of which isthe upper left corner of the screen in FIG. 4]. This position is sent tothe distance measurement frame controller 129 in the microcomputer 114as the coordinates of the center of the distance measurement frame.

The size of the distance measurement frame is decided as

a×b (where a is the horizontal width and b the vertical length of eachdistance measurement frame) by the distance measurement frame controller129, as illustrated in FIG. 4.

The distance measurement frame controller 129 decides the coordinates ofLR1, CR1, RR1, IR1 on the screen in accordance with the equations (1)shown below and sends these coordinates to the gate circuit 254 in theAF signal processing circuit 113, thereby controlling the distancemeasurement frames L, C, R.

 LR 1=(x−3a/2, y−b/1)

CR 1=(x−a/2, y−b/2)

RR 1=(x+a, y−b/2)

IR 1=(x+3a/2)  (1)

If a non-line-of-sight detection mode has been selected, the distancemeasurement frame position (x,y) is set at the center of the screen.When center-weighted distance measurement has been implemented, thevariable a, b which decide the size of the distance measurement frameare set to be comparatively large so that even a subject not located inthe center can be brought into focus stably.

If the line-of-sight detection mode has been selected, on the otherhand, the point stared is free to move about the screen and the size ofthe distance measurement frame is set to be comparatively small so as tobe able to reflect the intentions of the photographer. This limitssubjects. When the distance measurement frame position changes in theline-of-sight detection mode, the L, C, R frames move as one on thescreen. As a consequence, a case arises where the center position of theframe C does not coincide with the point stared at, as when the pointstared at is at one edge of the screen, and the reset signal generatingposition and data transfer signal generating position of each of the L,C, R frames cannot be determined with equations (1) as they are.

FIG. 5 is a diagram for describing how the reset signal generatingpositions and data transfer signal generating positions which decide thedistance measurement frames are defined in dependence upon a change inthe point stared at in the line-of-sight detection mode.

In FIG. 5, numeral 401 denotes the position of the point stared at, 501a point (x0, y0) at the upper left corner of the screen and 502 a point(x1, y1) at the lower right corner of the screen.

In a case where the point 401 stared at by the photographer is at thelower left of the screen (in a zone where the x coordinate falls withinthe range x0≦x<x0+a and the y coordinate falls within the rangey1−b/2≦y≦y1), the position of the distance measurement frame is set atthe lower left corner of the screen and the distance measurement framein which the point stared at resides is the frame L, as illustrated inFIG. 5. At this time the positions at which the signals that decide thedistance measurement frame positions are generated are as follows:

LR 1=(x0, y1−b)

CR 1=(x0+a, y1−b)

RR 1=(x0+2a, y1−b)

IR 1=(x0+3a, y1)  (2)

This is equivalent to substituting x=x0+3a/2, y=y1−b/2 into Equation(1).

Similarly, in a case where the point stared at resides at any point onthe screen, the relationship between the position at which the signalthat decides the distance measurement frame position is generated andthe distance measurement frame in which the point stared at is presentcan be classified into 5×3=15 areas by the positions of the x and ycoordinates of the point stared at (15 areas demarcated by the shadedareas on the screen shown in FIG. 5).

Shown below are transformation equations for the coordinates of theposition at which the frame-position decision signal is generated. Theseare obtained by transforming equations (1), where x and y are thecoordinate positions of the point stared at.

distance frame in which point stared at exists range x-coordinate of xtransformation measurement equation (1) x0 ≦ x < x0 + a x = x0 + 3a/2frame L (2) x0 + a ≦ x <0 + 3a/2 x = x0 + 3a/2 frame C (3) x0 + 3a/2 ≦ x< x1 − 3a/2 x = x frame C (4) x1 − 3a/2 ≦ x < x1 − a x = x1 − 3a/2 frameC (5) x1 − a/2 ≦ x ≦ x1 x = x1 − 3a/2 frame R range y-coordinate oftransformation y equation (1) y0 ≦ y < y0 + b/2 y = y0 + b/2 (2) y0 +b/2 ≦ y < y1 − b/2 y = y (3) y1 − b/2 ≦ y ≦ y1 y = y1 − b/2

If equations (1) are transformed in conformity with the area in whichthe point stared at resides, it is possible to determine the coordinatesof the position at which the frame-position decision signal is generatedand it is possible to ascertain whether the distance measurement framecontaining the point stared at is L, C or R.

The information relating to distance measurement frame status determinedas set forth above is supplied to the lens microcomputer 116 so thatstable, high-performance automatic focusing can be achieved in both theline-of-sight and non-line-of-sight detection modes of aninterchangeable lens system.

The distance measurement frame information supplied is, first of all,information as to whether the distance measurement frame selected byline of sight is the L, C oframe R R. If this information is notprovided, the lens microcomputer will not be able to determine which ofthe AF evaluation values obtained from the three distance measurementframes and delivered to the lens microcomputer is to be used for whichdistance measurement frame in execution of focal-point adjustment. Thismeans that the subject that the photographer wishes to focus on will notbe capable of being brought into focus.

The information further includes information as to whether the mode isthe line-of-sight detection mode or the non-line-of-sight detectionmode. The fact that the size of the distance measurement frame differsdepending upon the mode is as set forth above. However, since the numberof scanned lines on the screen picture varies depending upon the size ofthe distance measurement frame, the AF evaluation value also changes.

Accordingly, if the mode to switch the changeover has been made is notknown, a change in the evaluation value will always judged as being dueto a change in the subject and this will result in unstable automaticfocusing.

Further, since the AF evaluation value in the line-of-sight detectionmode in the case of a distance measurement frame of small size reactsmore sensitively in response to even a small change in the subject,automatic focusing lacking stability would result if AF control wereperformed in the same manner as in the non-line-of-sight detection mode.

The third item of information supplied to the lens assembly isinformation indicating which distance measurement frame position iscurrently changing in conformity with a change in the point being staredat. During movement of a distance measurement frame, the AF evaluationvalue fluctuates sharply even when there is no change in the distance tothe main subject. If AF control is performed on the basis of theevaluation value at such time, an erroneous operation will be carriedout and cause the photographer to experience discomfort, such as slightdefocusing from the focused state.

How the distance measurement frame information delivered to the lensassembly is used in AF control to prevent the above-mentioned problemsfrom occurring will be described later with reference to FIG. 6.

Described next will be how the microcomputer performs an automaticfocusing operation using the TE/FE peak evaluation value, TE line-peakintegration evaluation value, FE line-peak integration evaluation value,Y-signal peak evaluation value and Max-Min evaluation value in each ofthe distance measurement frames whose position/size has been decided. Itshould be noted that these evaluation values are transmitted to the lensmicrocomputer 116 in the lens assembly and that actual control isexecuted by the lens microcomputer 116.

The characteristics and usage of these evaluation values will now bedescribed.

The T/E peak evaluation value is an evaluation value which representsthe degree of focusing. Since this is a peak-hold value, it hascomparatively little dependence upon the subject, is influenced littleby blurring caused by camera movement and is ideal for determiningdegree of focusing and in judging restarting.

Though the TE line-peak integration evaluation value and FE line-peakintegration evaluation value also represent degree of focusing, theseare low-noise evaluation values stabilized by the effects of integrationand therefore are ideal for judging direction.

With regard to both the peak evaluation values and line-peak integrationevaluation values, the TE values extract higher high-frequencycomponents and therefore are ideal for use in a focusing operation inthe vicinity of the focused state. Conversely, the FE values are idealfor use far from the focused state when blurring is pronounced.Accordingly, these signals are added or are used upon being changed overselectively in dependence upon the TE level, thereby making it possibleto perform automatic focusing having a wide dynamic range from a highlyblurred state to the vicinity of the focused state.

The Y-signal peak evaluation value and Max-Min evaluation value aredependent upon the subject but not very dependent upon the degree offocusing. In order to judge the degree of focusing, judge restarting andjudge direction reliably, these evaluation values are ideal forascertaining a change in the subject, movement of the subject, etc. Thefocal-point evaluation value is used for the purpose of normalization inorder to eliminate the influence of a change in brightness.

In other words, whether a subject is a high-luminance or low-luminancesubject is judged based upon the Y-signal peak evaluation value, whethercontrast is high or low is judged based upon the Max-Min evaluationvalue and the size of the crests in the characteristic curves of theTE/FE peak evaluation value, TE line-peak integration evaluation valueand FE line-peak integration evaluation value are predicted andcorrected, thereby making possible optimum AF control.

These evaluation values are transferred from the camera body 128 to thelens assembly 127 and are supplied to the lens microcomputer 116 in thelens assembly 127 so that an automatic focusing adjustment may becarried out.

One example of a method of controlling focusing adjustment using theabove-mentioned distance measurement frame information delivered to thelens assembly will be described with reference to FIG. 6. The flowchartshown in FIG. 6 represents processing executed by the lens microcomputer116 in the lens assembly and is written with regard to an automaticfocusing algorithm of the AF program 117 at a specific focal length whenzooming is not being performed.

Though not illustrated, there is a processing routine separate from theprocessing of FIG. 6. In this separate processing routine, whichevaluation value from which distance measurement frame among the AFevaluation values within the three distance measurement frames deliveredfrom the microcomputer 114 in the camera body is stressed to performfocal-point adjustment is selected and processing is executedaccordingly.

AF control processing is started at step S601. Whether the prevailingmode is the line-of-sight detection mode is determined at step S602based upon the information delivered by the microcomputer 114 in thecamera body. If the prevailing mode is the non-line-of-sight detectionmode, then the program proceeds to step S606, where a wobbling operationfor the non-line-of-sight detection mode is carried out.

The prevailing mode is determined to be the line-of-sight detection modeat step S602, then it is determined, on the basis of the distancemeasurement frame information delivered by the microcomputer 114,whether the distance measurement frame is currently moving (step S603).If the distance measurement frame is moving (“YES” at step S603), thesystem stands by with the focusing lens being held at rest. At thecompletion of movement, wobbling for the line-of-sight detection mode isperformed at step S604.

The wobbling operation performed at the time of the line-of-sight andnon-line-of-sight detection modes will be described with reference toFIGS. 7A through 7D.

FIG. 7A is a diagram illustrating the change (701) in the level of theAF evaluation value obtained when the focusing lens is moved frominfinity to close-up with respect to a given subject. The position ofthe focusing lens is plotted along the horizontal axis and the AFevaluation value is plotted along the vertical axis. The point at whichfocus is achieved is point 702, at which the AF evaluation value is atthe maximum level. (The position of the in-focus focusing lens is point708.) The position of the focusing lens is controlled in such a mannerthat the AF evaluation value is maximized at all times. A wobblingoperation is performed to determine whether the in-focus point is on theside in the direction of close-up or the side in the direction ofinfinity.

The wobbling operation is an operation for accepting the AF evaluationvalue while driving the focusing lens slightly to determine whether thecamera is currently in focus or out of focus (i.e., to determine whetherthe in-focus point is on the side in the direction of close-up or theside in the direction of infinity when the camera is out of focus). Forexample, if the current focusing position is on the side of infinity(position 709) with respect to the in-focus point, the wobblingoperation is executed to move the lens slightly from the direction ofinfinity (the focusing lens position is moved as shown at 703, with thetime axis extending into the page). When this is done, the AF evaluationvalue obtained is as indicated at 704.

If the focusing lens position is on the close-up side with respect tothe in-focus position (position 710), the lens is driven slightly in themanner shown at 705. When this is done, the AF evaluation value isobtained as indicated at 706. Since the phases of the change in signallevel with respect to a change in the same driving direction of thefocusing lens are opposite to each other at 704 and 706, discriminatingthis fact makes it possible to ascertain the focusing-lens drivedirection in which the in-focus point is present.

Further, when the lens is driven slightly (711) at the summit of thecrest 701, the AF evaluation value (712) obtained has a small amplitudeand is different in shape. As a result, whether the camera is out offocus or in focus can be determined.

With wobbling in the vicinity of the in-focus point, the photographersees a blurred image depending upon the amplitude of drive (α in FIG.7A). Accordingly, it is required to establish the minimum amplitude atwhich the evaluation value is satisfactorily obtained.

On the other hand, there are cases where an evaluation value amplitudesufficient for judging direction is not obtained at the foot of thecrest 701 even if the focus lens is driven slightly. Accordingly, it isdesired that the amplitude of lens drive be made comparatively large inthis region.

In the non-line-of-sight detection mode, it is presumed that the subjectphotographed will undergo a major change when the photographer operatesthe camera as by panning the camera. The AF evaluation value at thistime changes from the level at the summit of the crest, at which a givensubject is in focus, to the level at the foot of the crest of anothersubject. Accordingly, it is required that the amplitude α of minutedrive in the wobbling operation be enlarged to a certain extent.

On the other, in the line-of-sight detection mode, it is presumed thatthe point at which the photographer gazes will move with regard to asubject appearing in the finder. Since an AF evaluation value of acertain level can be obtained even when the main subject moves, it isdesired that the amplitude α of minute drive be made as small aspossible.

Accordingly, the driving amplitude a in the wobbling operation is set,as shown in FIG. 7B, in dependence upon the depth of field (lensopening), with the values of α in the line-of-sight detection modediffering from those in the non-line-of-sight detection mode.

In FIG. 7B, δ represents the circle of least confusion. No blurringresults if the position of the focusing lens is moved from the in-focusposition by an amount equivalent to δ or less. In other words, at stepS606 in FIG. 6, wobbling is performed using the value of a prevailing inthe non-line-of-sight detection mode in FIG. 7B. At step S604, wobblingis performed using the wobbling amplitude set by α in the line-of-sightdetection mode in FIG. 7B.

During movement of the distance measurement frame, the wobblingoperation is not carried out, as set forth above in connection with stepS603.

This is to prevent a situation in which, when the photographer is in theprocess of moving the point stared at up to the intended main subject,bringing subjects encountered along the way into focus would be contraryto the intent of the photographer. Further, this is to prevent asituation in which blurring is induced. Specifically, during movement ofthe line-of-sight distance measurement frame, a subject may no longer bepresent in the frame or, even if it is present, the output of thein-focus evaluation value is not obtained satisfactorily or the signalfluctuates sharply because the distance measurement area is moving.Direction cannot be discriminated correctly in this state, even if thewobbling operation is performed, and erroneous operation results. Thisbrings about blurring.

Further, there is a good possibility that the main subject has changedwith movement of the point stared at. Accordingly, the wobblingoperation is performed at the end of movement of the distancemeasurement frame for the purpose of verifying that the in-focus statehas been attained.

Step S60 in FIG. 6 is for setting speed of focusing movement forhill-climbing of the curve in the line-of-sight detection mode.

In a case where the non-line-of-sight detection mode has been determinedat step S602, the above-described wobbling operation is carried out atstep S606 and then focusing speed for hill-climbing at the time of thenon-line-of-sight detection mode is set at step S607.

As mentioned above, a highly blurred state readily occurs if the cameraperforms an operation such as panning in the non-line-of-sight detectionmode. It is desired, therefore, that the focusing lens be driven as fastas possible to shorten the time needed to achieve the focused statewithout the in-focus point being reached from the foot of the crest ofthe characteristic curve 701 of the in-focus evaluation value shown inFIG. 7A.

In the line-of-sight detection mode, on the other hand, the range offluctuation of the AF evaluation value is small in comparison with thatwhich prevails at the time of non-line-of-sight detection mode (thefluctuation occurs frequently because the distance measurement frame issmall), and hill-climbing is from the mid-portion of the crest of thecharacteristic curve 701. Consequently, when the speed of hill-climbingis too high, considerable defocusing accompanies a mistake in terms ofdirection of hill-climbing and the photographer realizes that thein-focus direction has been passed. (In the non-line-of-sight detectionmode, the highly blurred state will already exist even if the in-focusdirection has been mistaken for the opposite direction. Thephotographer, therefore, tends not to notice.) Accordingly, the speed offocusing movement for hill-climbing is set in dependence upon whetherthe mode is the line-of-sight detection mode or non-line-of-sightdetection mode.

It is determined at step S608 whether the result of the wobblingoperation performed at step S604 or S606 is that the camera is currentlyin focus or out of focus. If it is determined that the camera is infocus, movement of the focusing lens is stopped and a transition is madeto a processing routine for monitoring restart. The routine starts fromstep S613.

If the decision rendered at step S608 is that the camera is out offocus, then the program proceeds to step S609. Here hill-climbing in thedirection which is the result of judgment based upon the wobblingoperation is executed at the focusing speed set by step S605 or S607.

It is determined at step S610 whether the in-focus point, i.e., thesummit of the in-focus evaluation signal, has been exceeded.Hill-climbing continues if it has not been exceeded. If it has beenexceeded, the focusing lens is returned to the summit (steps S611, 612).

There are also cases where the subject changes owing to panning or thelike during the operation for returning to the summit. Accordingly, ifthe focusing lens has at last attained the summit, it is determinedwhether the current position is truly the summit, i.e., the in-focuspoint. To accomplish this, the program returns to the processing fromstep S602 onward, movement of the line-of-sight frame is monitored andthe wobbling operation is performed again.

If the camera is judged to be in focus at step S608, the programproceeds to the processing from step S613 onward, namely the routine formonitoring restart.

If the prevailing mode is judged to be the line-of-sight detection mode(“YES” at step S614), it is determined at step S615 whether the distancemeasurement frame is moving. If the frame is moving (“YES”at step S615),the program returns to step S603 so that processing for verifying thein-focus state is executed after the end of movement.

If it is found at step S615 that the distance measurement frame is notmoving, restart for the line-of-sight detection mode is determined atstep S616. Since the distance measurement frame is small, thefluctuation in the level of the AF evaluation value occurs frequentlyowing to subjects moving into and out of the frame. This is taken intoaccount at step S616 so that the restart operation is made moredifficult than in the case of the weighted-center distance measurementframe in the non-line-of-sight detection mode, thereby improving thestability of the line-of-sight AF operation.

Operation will be described in detail with reference to FIG. 7A. Assumethat the focusing lens is at position 708 and that the level of the AFevaluation value at this time is 702, as shown in FIG. 7A. The level at702 corresponds to the AF evaluation value level stored at step S613 inFIG. 6.

The level of the evaluation value declines from 702 to 707 owing to achange in the subject. The determination as to whether restart is to beexecuted at this time is performed in the following manner:

If the level of the evaluation value has changed from the level of 702by an amount in excess of a restart threshold value β, then it isdetermined to execute restart. If the amount of fluctuation in theevaluation value is less than the restart threshold value β, thedecision rendered is not to execute restart.

The threshold value β is set to different values for the line-of-sightdetection mode and non-line-of-sight (at steps S616 and S617 in FIG. 6),as illustrated in FIG. 7C. Using the in-focus AF evaluation value levelthat has been stored at step S613 is adopted as a reference, thesettings are made in such manner that restart is executed if the changeis greater than 40% of this value in the line-of-sight detection mode orgreater than 20% in the non-line-of-sight detection mode.

With reference again to FIG. 6, step S615 is as described above. Thereason for not executing the restart decision processing of step S616during movement of the distance measurement frame detected at step S615is to assure that restart will not occur each time the point stared atis moved. This is necessary because the AF evaluation value obtainedfrom within the frame fluctuates during movement of the distancemeasurement frame, as already described.

For example, if the restart decision is allowed during movement of theline-of-sight frame, the AF evaluation value will fluctuate owing tomovement of the distance measurement frame even though moving thefocusing lens is unnecessary, as when the line of sight is moved withrespect to a subject for which there is no change in distance. Theresult is restart, which is accompanied by the occurrence of defocusing.

The result of the decision rendered at step S616 or S617 isdiscriminated at step S618. In case of non-restart, the focusing lens ishalted as is (step S619) and the program returns to step S614, whererestart monitoring is performed again.

If restart is discriminated at step S618, then the program returns tostep S602, where the wobbling operation is performed again and directionof movement is discriminated. By repeating this operation, the focusinglens is operated so as to maintain the focused state at all times.

In the loop of this automatic focusing operation, the degree to whichvelocity control is applied using the TE/FE peak, the absolute level ofthe crest summit judgment and the amount of change in the TE line-peakintegration evaluation value are better for predicting the size of thecrest than is judgment of the subject using the Y-peak evaluation valueand Max-Min evaluation value, and prediction is based upon these.

Modification of First Embodiment

FIG. 8 is a diagram illustrating the construction of a modification ofthe first embodiment of the invention. In the first embodiment, thedistance measurement frame setting position is determined by detectingline of sight. In this modification, an example is described in which avideo information acceptance area is decided by auxiliary input means,which serves as pointing means, rather than by line-of-sight input.Other elements are the same as those in the first embodiment, areindicated by reference characters the same as those used in FIG. 1 andneed not be described again; only the aspects that distinguish thismodification from the first embodiment will be described.

Video-information acceptance area setting information accepted by avideo-information acceptance area position setting unit 801 is processedby a video-information acceptance area detecting/setting circuit 802 andthe processed information is sent to the microcomputer 114 in the camerabody.

In dependence upon the status of a switch 803 for effecting a transitionto a mode for varying the video-information acceptance area, themicrocomputer 114 decides whether or not to use the video-informationacceptance area from the area detecting/setting circuit 802 and sendsthe distance measurement frame information decided by the distancemeasurement frame controller 129 to the AF signal processing circuit 113and lens microcomputer 116.

The video-information acceptance area position setting unit 801 may bean ordinary keyboard, a mouse, a track ball or a joystick used as theinput devices of a computer.

Second Embodiment

A second embodiment of the invention will now be described. Thisembodiment differs from the first embodiment in that the AF signalprocessing circuit and distance measurement frame controller areprovided in the lens assembly. In other aspects the system configurationis the same as that of the first embodiment and these aspects need notbe described again. The description will focus on the aspects thatdistinguish this embodiment from the first embodiment. Elements of thisembodiment identical with those of the first embodiment are designatedby like reference characters.

In FIGS. 10 and 11, a microcomputer 114A sends a lens microcomputer 116Ain the lens assembly 127 the line-of-sight position information and thestatus of the line-of-sight detection mode switch 141. In order to allowthe photographer to recognize the point currently being stared at in theline-of-sight detection mode, a video signal and information indicatingthe position stared at are mixed by the LCD display circuit 133 and theline-of-sight position is displayed on the screen of the LCD monitor134.

In a case where the line-of-sight detection mode has not been selectedby the line-of-sight detection mode switch 141, the microcomputer 114Asends line-of-sight input function inhibiting information to theline-of-sight detecting circuit 140, inhibits display of theline-of-sight position and delivers the center position of the imagescreen to the lens microcomputer 116A, together with the line-of-sightswitch information, as pseudo-line-of-sight position.

The video signal which enters the camera signal processing circuit 112is converted to a standard television signal and, at the same time, thecircuit 112 outputs a gamma-corrected video signal S3 in which R, G, Bsignals have been mixed. The signal S3 enters a video signal normalizingcircuit 143.

The video signal normalizing circuit 143 normalizes the video signal S3by making the video signal level the same, regardless of the camera,when the same subject is photographed. The normalized video signal isoutputted as signal S4.

The normalized video signal S4 is sent from a camera body 128A to a lensassembly 127A via a lens mount.

The lens assembly 127A applies the normalized video signal S4 from thecamera body 128A to an AF signal processing circuit 113A, which proceedsto generate an AF evaluation value. The AF evaluation value generated bythe AF signal processing circuit 113A is read by the data readoutprogram 115 in the lens microcomputer 116A. The AF signal processingcircuit 113A corresponds to the extracting means for extracting thefocal-point signal according a feature of the present invention.

A distance measurement frame controller 129A in the lens microcomputer116A decides the position and size of the focal-point detection area(distance measurement frame) in conformity with the line-of-sightinformation and status of the line-of-sight detection switch 141 sentfrom the microcomputer 114A in the camera body, and controls the AFsignal processing circuit 113A on the basis of the decided distancemeasurement frame information in accordance with the data readoutprogram 115A, thereby extracting the AF evaluation value, whichcorresponds to the position of the point being stared at, from thenormalized video signal sent from the camera body.

The states of zoom switch 130 and AF switch 131 are transferred from themicrocomputer 114A to the lens microcomputer 116A.

From this point onward the lens microcomputer 116A performs a zoomingoperation and focusing operation in a manner similar to that of thefirst embodiment.

Modification of Second Embodiment

FIG. 12 is a block diagram illustrating a modification of the secondembodiment of the present invention. This arrangement is similar to thatof FIG. 10 except for the fact that the line-of-sight detection means isnot provided. The alternative means, namely the auxiliary input means,also is the same as the auxiliary input means according to themodification (FIG. 8) of the first embodiment and need not be describedagain.

In accordance with the first embodiment, as described above, a videocamera system having an interchangeable lens assembly is so adapted thatthe setting of an image-information acceptance area on a screen pictureand the extraction of image information corresponding to this area arecarried out on the side of the camera body, information relating to thearea and image information are transmitted to the side of the lensassembly and control based upon these items of information is performedon the side of the lens assembly.

In accordance with the second embodiment, an image signal andinformation representing a designated position in the screen picture aresupplied from the side of the camera body to the lens assembly. On theside of the lens assembly, an image-information acceptance area on thescreen is controlled based upon the position information, and the stateof the image sensing operation is controlled based upon the image signalcorresponding to the image-information acceptance area. As a result,optimum response can be determined for individual lens assemblieswithout increasing the load on the camera side. This makes it possibleto realize a camera system which makes it possible to control,accurately and stably, the imaging of various subjects and a mainsubject under various photographic conditions.

Further, since control processing for zooming and focusing is executedon the side of the lens assembly, it is unnecessary to provideinformation for various lens assemblies entirely on the side of theimage sensing apparatus, thus alleviating the processing load on theside of the main body of the imaging apparatus.

In particular, the focal-point evaluation value and the informationrelating to the setting of the focal-point detection area are deliveredfrom the side of the image sensing apparatus to the side of the lensassembly and the controls for automatic focusing are provided on theside of the lens assembly. As a result, even if a variety of lensassemblies are capable of being attached, optimum response can bedetermined for each individual lens assembly. Moreover, it is possibleto realize both the automatic focusing performance of ordinaryweighted-center distance measurement and the features of a focal-pointdetection area setting method, which relies upon pointing means usingexternal input means such as line-of-sight detection. This makes itpossible to suitably adjust the focus of a main subject aimed at by thephotographer.

Further, information indicating whether the focal-point detection areais currently changing and information representing focusing adjustmentmode desired by the photographer is supplied as information relating tothe focal-point detection area, and operation by focusing adjustmentcontrol is altered in conformity with this information. This makes itpossible to prevent a variety of erroneous operations that tend to occurduring movement of the focal-point detection area.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

What is claimed is:
 1. A camera having an interchangeable lens assemblycapable of processing an image signal, comprising: image sensing means,provided in a camera body, for converting an image of a subject formedon an image sensing plane to an image signal and outputting the imagesignal; pointing means, provided in said camera body, for pointing toany position in the image sensing plane; area setting means, provided insaid camera body, for setting a prescribed area at said any positionpointed to by said pointing means; extracting means, provided in saidcamera body, for extracting a prescribed signal component from the imagesignal corresponding to the prescribed area set by said area settingmeans, and generating an evaluation value relating to an imaged state ofthe image; and transmitting means, provided in said camera body, fortransmitting information relating to a position of the prescribed areaset by said area setting means and the evaluation value, to imageprocessing means provided in said lens assembly, for performing apredetermined image processing for controlling a state of the image. 2.The camera according to claim 1, wherein said prescribed area is afocal-point detection area for detecting a focal point of said lensassembly, and the evaluation value relating to an imaged staterepresents state of focus of said lens assembly.
 3. The camera accordingto claim 2, wherein said pointing means points to said any position bydetecting position of operator's line of sight directed into thepicture.
 4. The camera according to claim 2, wherein said pointing meansis a pointing device such as a keyboard, mouse, track ball or joystick.5. A camera having an interchangeable lens assembly capable ofprocessing an image signal, comprising: image sensing means, provided ina camera body, for converting an image of a subject formed on an imagesensing plane to an image signal and outputting the image signal;pointing means, provided in said camera body, for pointing to anyposition in the image sensing plane; first area setting means, providedin said camera body, for setting a first focal point detecting area atsaid any position pointed to by said pointing means; second area settingmeans, provided in said camera body, for setting a second focal-pointdetecting area at a prescribed position in the image sensing plane;selecting means, provided in said camera body, for selecting said firstarea setting means or said second area setting means; extracting means,provided in said camera body, for extracting a prescribed signalcomponent from the image signal corresponding to a focal-point detectionarea set by said first area setting means or second area setting means,whichever has been selected by said selecting means; and transmittingmeans, provided in said camera body, for transmitting informationrelating to the focal-point detection area, position informationrepresenting status of a first focal detecting area of said first areasetting means, the evaluation value and selection information from saidselecting means to image processing means, provided in said lensassembly, for performing a predetermined image processing.
 6. A lensassembly capable of being attached to and detached from a camera,comprising: drive means for driving a lens possessed by the lensassembly; receiving means for receiving, from the camera, an evaluationvalue extracted from an image signal relating to an imaged state of animage imaged by the camera, position information relating to a set areain the picture and information representing operation of the set area;and control means for processing the evaluation value and the positioninformation relating to the set area received by said receiving meansand controlling said drive means based upon the processed plurality ofinformation.
 7. The lens assembly according to claim 6, wherein said setarea is a focal-point detection area for detecting the focal point ofsaid lens assembly, and the evaluation value relating to an imaged staterepresents state of focus of said lens assembly.
 8. The lens assemblyaccording to claim 7, wherein said control means inhibits a controloperation during a change in said focal-point detection area.
 9. Thelens assembly according to claim 8, wherein said control means changesthe control operation to a prescribed operation when the change in saidfocal-point detection area has ended.
 10. An interchangeable lens-typevideo camera system comprising a camera and an interchangeable lensassembly, said camera including: image sensing means for converting animage of a subject formed on an image sensing plane to an image signaland outputting the image signal; pointing means for pointing to anyposition in the image sensing plane; area setting means for setting aprescribed area at said any position pointed to by said pointing means;extracting means for extracting a prescribed signal component from theimage signal corresponding to the prescribed area set by said areasetting means, and generating an evaluation value relating to the imagedstate of said image; transmitting means for transmitting positioninformation of the prescribed area set by said area setting means andthe evaluation value to the lens assembly; and said lens assemblyincluding: receiving means for receiving position information of theprescribed area and the evaluation value from said camera; drive meansfor driving a lens possessed by said lens assembly; control means forcontrolling said drive means based upon the position information of theprescribed area and the evaluation value received by said receivingmeans.
 11. The system according to claim 10, wherein said prescribedarea is a focal-point detection area for detecting a focal point of saidlens assembly, and the evaluation value relating to an imaged staterepresents state of focus of said lens assembly.
 12. The systemaccording to claim 11, wherein said control means inhibits a controloperation during a change in said focal-point detection area.
 13. Thesystem according to claim 12, wherein said control means changes thecontrol operation to a prescribed operation when the change in saidfocal-point detection area has ended.
 14. The system according to claim10, wherein said pointing means points to said any position by detectingposition of operator's line of sight directed into the picture.
 15. Thesystem according to claim 10, wherein said pointing means is a pointingdevice such as a keyboard, mouse, track ball or joystick.
 16. A camerahaving an interchangeable lens assembly capable of processing an imagesignal, comprising: image sensing means, provided in a camera body, forconverting an image of a subject formed on an image sensing plane to animage signal and outputting the image signal; pointing means, providedin said camera body, for pointing to any position in the the imagesensing plane; and transmitting means, provided in said camera body, fortransmitting an image signal, outputted by said image sensing means andposition information relating to said any position pointed to by saidpointing means to image processing means, provided in said assembly, forperforming a predetermined image processing for controlling a sate ofthe image.
 17. The camera according to claim 16, wherein said pointingmeans points to said any position by detecting position of operator'sline of sight directed into the picture.
 18. The camera according toclaim 16, wherein said pointing means is a pointing device such as akeyboard, mouse, track ball or joystick.
 19. The camera according toclaim 16, further comprising normalizing means for normalizing the imagesignal before the image signal is transmitted by said transmittingmeans.
 20. A camera having an interchangeable lens assembly capable ofprocessing an image signal, comprising: image sensing means, provided ina camera body, for converting an image of a subject formed on an imagesensing plane to an image signal and outputting the image signal;pointing means, provided in said camera body, for pointing to anyposition in the image sensing plane; selecting means, provided in saidcamera body, for selecting on/off of operation of said pointing means;and transmitting means, provided in said camera body, for transmitting,to image processing means provided in said lens assembly, the imagesignal outputted by said image sensing means and position informationrelating to said any position in the picture pointed to by said pointingmeans when said pointing means is on or information relating to apredetermined prescribed position when said pointing means is off.